The present invention relates to a liquid crystal display device (LCD) and more particularly, to a backlight illumination unit for the LCD.
In a liquid crystal display, a light is applied to a display member from the back side of the display member where there is not sufficient ambient light impinging onto the front for viewing the display on the device. An observer sees the transmitted through light as displayed information.
For backlighting, a luminous member is located behind the liquid crystal display member. The luminous member generates light which is applied to the back of liquid crystal display member and an observer sees the displayed information as bright and dark regions illuminated by light transmitted through liquid crystal display member. The liquid crystal display member selectively allows portions of display member to transmit light whereas other portions of display member are opaque and prevent transmission of light. When liquid crystal display devices are used in toys, watches, and other portable battery powered devices, it is necessary to provide an illumination device which is operable for long periods of time, which has a relatively large panel area, and which is electrically power efficient.
A liquid crystal display device having a backlight unit with a small lamp has been employed for wristwatches. The backlight for such a wristwatch display is used to illuminate the face of the watch to make it possible to read the time at night. Conventional types of backlights for liquid crystal display devices are not fully satisfactory in brightness, illumination intensity uniformity, and long battery life.
A relatively large amount of electrical power is needed to provide energy to the luminous member, at least a much larger amount than necessary to power the LCD itself. Thus the power needed to drive a luminous member is of considerable importance. Even if this power consumption is reduced to less than 1 watt, the power used to backlight liquid crystal display member is not neglegible, especially where dry cell batteries are used as the power source, battery life is significantly shortened as a result of the power used to drive the luminous member.
Accordingly, there is a need to increase the battery life of a portable liquid crystal displays using backlighting for viewing situations where there is insufficient ambient light to produce a viewable display. It is also desirable to improve the efficiency of the backlight as well as the uniformity of the illumination in order to reduce battery drain.